基于相位一致性和方向滤波冕环震荡识别与跟踪

Identification and Tracking of Coronal Loop Oscillation Using Phase Congruency and Directional Filter

冕环结构的准确识别和跟踪有利于更好地研究和分析冕环特征以及同耀斑爆发和日冕物质抛射之间的关系。提出基于相位一致性和方向滤波的冕环震荡识别和跟踪方法。识别过程如下:首先,使用相位一致性技术对太阳图像中的冕环特征进行识别;其次,对识别后的图像进行二值化处理;接着使用方向滤波去除非冕环的结构特征;然后,对其进行形态学处理;最后,再对识别结果进行二次曲线拟合。运用所提算法对2011年9月6日由太阳动力学观测站(Solar Dynamics Observatory,SDO)在Fe IX 17.1 nm波段观测到的冕环震荡进行了识别和跟踪,结果验证了所提算法的可行性和准确性。证明所提算法能被用于冕环特性以及震荡过程的研究和分析。

Solar flares occurring usually cause oscillations of nearby coronal loops. A precondition of studying these oscillations is to explore how to identify coronal loops. Meanwhile,accurate identification is also crucial to study and analyze the statistical features of the coronal loops and the relationship to coronal magnetic field. However,the traditional identification methods based on intensity and / or gradient threshold have some limitations,because coronal loops hold a relatively low contrast,blurred boundary,and the image noise is close to coronal loops. So we propose a new method to identify coronal loops using phase congruency and directional filter. The identification procedures are as follows： firstly,phase congruency technique is used to identify linear shape in a coronal image; secondly,a binary image is obtained from the image of phase congruency for detecting the loop features; thirdly,a directional filter based on Sobel Operator is applied to remove the redundant features that are nearly perpendicular to those target loops; fourthly,morphological filters are used to extract the shape of those loops; finally,quadratic fitting is used to smooth the identified loop features. For illustrating the performance of the method,the coronal loop oscillations taken with the Atmospheric Imaging Assembly on aboard the Solar Dynamic Observatory on September 11,2011 are used to evaluate the identification and tracking process. The coronal loop oscillations were caused by a nearby X2. 1flare emission. We analyzed the identified results,and calculated their oscillation period,phase difference and decay coefficient. They are in good agreement with those of previous works. This implies that the proposed method can accurately identify the shape of a loop in an image; furthermore,the results can also be used to study the physical properties of coronal loop oscillations and the relationship to others solar phenomena.